Warming set to 'devastate' coral
By Paul Rincon
BBC News science reporter



Dead reefs collapsed and became covered in algae
Rising ocean temperatures look set to cause lasting devastation to coral reef systems, a study suggests.

An international team of researchers looked at reefs in the Seychelles, where an ocean warming event in 1998 killed much of the live coral.

The group found the oceanic reef had experienced fish extinctions, algal growth, and only limited recovery.

Details have been published in the US journal Proceedings of the National Academy of Sciences.

The 1998 event saw Indian Ocean surface temperatures rise to unprecedented levels, killing off - or "bleaching" - more than 90% of the inner Seychelles coral. Coral bleaching has been described as a vivid demonstration of climate change in action.

"[Bleaching events] are becoming more frequent and are predicted to become more severe in coming decades. They are directly linked to increases in sea surface temperatures," said lead author Nick Graham, of the University of Newcastle, UK.

'Special relationship'

Corals live in a mutually beneficial relationship with photosynthetic algae. But when sea surface temperatures at a given location rise above summer limits, the corals expel their single-celled bedfellows (possibly because the algae start producing toxins).

Algae provide corals with most of their energy and their colour - hence the term bleaching. If the high temperatures are prolonged, the corals start to die off en masse.


How healthy coral should look
Bleaching in 1998 occurred in all reef regions of the world; 16% of the world's reefs were lost in that one year, alone. But the western Indian Ocean suffered most because of an interaction between El Nino and another periodic climate phenomenon called the Indian Ocean dipole.

In the seven years since, the damaged reefs have been largely unable to reseed. Many simply collapsed into rubble and became covered in algae.

This collapse removed food and shelter from predators for a large and diverse amount of marine life. The survey showed four fish species could already be locally extinct, and six species are at critically low levels.

The survey also revealed that the diversity of fish species in the heavily impacted sites had plummeted by about 50%.

Computer models

Reduced biodiversity makes for a more fragile, less stable ecosystem.

The team says smaller fish have fallen in number more rapidly than larger species, but their decreased availability is having a more lasting effect on the food chain - and this effect is likely to be amplified as time goes on.

Moreover, the group's paper reports, the observed fall in herbivorous fish is a key concern, as they control algal spread.

The problems seem to be down to the relative isolation of coral systems in this area. An absence of nearby reefs to provide larvae which could settle and grow into new coral structures, along with the lack of favourable sea currents to transport the larvae, could be largely to blame.

In expansive continental reef systems such as the Great Barrier Reef in Australia, there exists more potential for so-called "refugia" which may escape the worst of the bleaching. In these areas, corals could survive and subsequently go on to repopulate the worst-hit areas.

But the prospects may not be so good if bleaching events become more common and more severe, the team says.

Since 1998, another three bleaching events have been recorded in the Indian Ocean and at least two in the Pacific.

"Various [computer simulations] suggest we'll be having a 1998-scale bleaching event annually within 30 years, so the outlook is pretty bleak for how common these events will become," said Dr Graham.

Worldwide, coral reefs cover an estimated 284,300 sq km and support over 25% of all known marine species.

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I dont undertand you frogfish...AND YOU SAY GLOBAL WARMING IS A POINTLESS TOPIC?

Hmmm


I don't see the word Global Warming here...

Rising sea levels can be attributed to other factors

Okay, where does a rising sea level come from,-wouldn't that involve water of some sort at some point?? I understand erosion could be a factor, but if that's the case, wouldn't the earth be going through somewhat radical changes due to geological shifts, etc.?

Okay, where does a rising sea level come from,-wouldn't that involve water of some sort at some point?? I understand erosion could be a factor, but if that's the case, wouldn't the earth be going through somewhat radical changes due to geological shifts, etc.?


Server problem-sorry for duel reply...

Warm temperatures are probably the biggest contributer to coral bleaching. That is why El nino events cause a lot of bleaching. If a few degrees warming from El nino events (which are only temperary rises in temperatures) cause so many incidents of bleaching, wait to the ocean temperatures increase for substained periods of time

Agreed, but it is not contributed to Global Warming...

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i think it's pretty clear the cause i mean if you want to ignore it that's your decision but if they've lasted this long with "natural" rising tempratures why is it such a problem now?
many estimates put the time it took for many of the reef in the 10s of thousands of years... and yet only now are they so threatened that in in the next 10 years they could be wiped out completely...
sound like global warming to me....

Interesting little chat i had tonight with a friend of mine who is a enviormental engineer, the subject was global warming, as you are aware manapa some feel its a myth (points up)
I wonder how does one miss the obvious?????Its a very serious issue regardless whether one thinks so or not, and you may like to Know that at this time ther are alot of good people working for the ecosystem.......

that is good to know, but there are also quite a few that are out to sway public opinion... even so far as to creat ads for tv that show carbon dioxide in a good light....
i just hope for once the enviornment triumps over the one with the most money....

it will when the environment collapses and we go extinct. then the planet will heal its self and move on.

yeah it might be better for the rest of the world....
not that i want us to die out...

a .5 degree change is serious?

it depends on your source i guess....
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